The invention relates to an apparatus for cleaning a photosensitive member of an electrophotographic copying machine of the type employing a wet developing process to produce a visual image which is transfered onto a transfer sheet.
In an electrophotographic copying machine, an electrostatic latent image is formed on a photosensitive member and is developed to form a visual image, which is transfered onto a record sheet. Since the single photosensitive member is repeatedly used, there is a need for the provision of an apparatus for cleaning the surface of the photosensitive member for each copying cycle so that any residual toner may be removed therefrom in readiness for a new copying cycle after the visual image has been transfered onto the record sheet. If the residual toner is allowed to remain on the surface of the photosensitive member after completion of the transfer step, it may cause a marring of the record sheet during the next copying cycle or it may be firmly adhered to the surface of the photosensitive member to degrade its functioning. Usual cleaning technique employs a relatively thin blade of a resilient material, the edge of which is held in abutment against the surface of the photosensitive member to remove any residual toner therefrom, and such technique is particularly effective in an electrophotographic copying machine of a wet developing type. It is customary to supply a cleaning liquid to the surface of the photosensitive member adjacent the edge of the blade on the side the toner is removed, in order to ensure a smooth movement of the photosensitive member relative to the blade and to flush away any residual toner which is scraped off the surface thereof. In order to achieve an intended cleaning effect, it is necessary to hold the blade under pressure against the surface of the photosensitive member, but such blade pressure may frequently cause a damage to the photosensitive member. In order to avoid such drawback, it has been proposed to dispose a releasing member of soft material such as sponge or felt, which can be wet by the cleaning liquid, in contact with the surface of the photosensitive member so that any residual toner can be freed or released from the surface thereof before it is scraped off by the blade. Such an arrangement is shown in FIG. 1, which will be described below.
Referring to FIG. 1, the cleaning apparatus shown essentially comprises a blade 1, a releasing member in the form of a roller 2, made of sponge material, and a pipe 3 for supplying a cleaning liquid 4. The blade 1 is disposed so that its edge is held in abutment against the surface of a phootosensitive member 10 which is shown as a drum while its other edge is held by a holder 1'. The roller 2 has a rotary shaft which is disposed substantially parallel to the rotary shaft of the drum 10, and is disposed in abutting relationship with the surface of the drum 10 in a manner such that its region of contact undergoes an elastic deformation. In operation, before the drum 10 is set in motion, a quantity of cleaning liquid 4 is supplied through the pipe 3 to the cleaning station, that is, that portion of the surface of the drum which is defined between the blade 1 and the roller 2. Part of the cleaning liquid 4 may be bled from the piping 3 to be supplied to the roller 2 directly, as by passing it through its rotary shaft which is made hollow and formed with a multiplicity of apertures. The cleaning liquid 4 supplied forms a pool in the cleaning station, wetting the roller 2. The remaining portion of the cleaning liquid freely falls off the opposite ends of the drum or is collected into a suitable liquid reservoir through drainage ducts disposed at such end, as well known in this field of the art. The cleaning liquid usually comprises a developing solution or matrix therefor. As the drum 10 is set in motion and a copying operation proceeds to complete a transfer of the visual image onto the record sheet, the surface portion of the drum 10 to which a residual toner is left deposited reaches the position of the roller 2. Roller 2 rotates in the opposite direction from the drum while squeezing its impregnated cleaning liquid 4 into the area of its contact with the drum surface, thus releasing any residual toner which attaches to the drum surface, by its rubbing action. The released toner is then flushed away by the cleaning liquid 4 which is supplied through the pipe 3, and any remaining toner is completely scraped off the drum surface by the blade 1 to be carried away by a flow of the cleaning liquid 4 falling off the opposite ends of the drum. The supply of the cleaning liquid 4 is continued in the meantime, thus maintaining the wetting on roller 2. With this apparatus, since the toner is initially moistened or rendered readily separable from the drum surface by the releasing member of roller 2, the pressure with which the blade 1 is held against the drum can be substantially reduced, thus almost completely avoiding damage to the drum which may be caused by the blade 1.
However, when a series of copying cycles is terminated, and a new copying operation is initiated after a pause, the level of the cleaning liquid in the cleaning station may temporarily rise and sometimes an overflow, over the blade 1 may occur (see FIG. 2) as the cleaning liquid 4 is supplied through the pipe 3 if the roller 2 is already sufficiently wet. As the drum 10 and the roller 2 rotate to squeeze the cleaning liquid which is retained in the roller, and as the drum surface moves to cause a flow of the liquid and the rotation of the roller 2 causes ripples, the overflow of the cleaning liquid may be further increased. Such a phenomenon is particularly noticeable in a cleaning apparatus of the type in which the supply of the cleaning liquid is continued independently from the motion of the drum during the time the master switch of the copying machine is turned on. Such an overflow of the cleaning liquid may run down the drum surface, as shown at 4', to cause a non-uniformity in the charging or insufficient exposure, producing a trace pattern on the record sheet obtained.